Touch points, friction coefficients, form factors, and the two hysteresis factors are adapted for clutches using algorithms. Characteristic curve relations are used to evaluate torque as a function of the position and to determine the position as a function of the torque.
Only the touch point is determined at the initial start of operation, since the touch point is very slow to adapt and an erroneous touch point has a considerable effect in particular in start-up and shifting processes. For this purpose, a routine has been developed that allows the determination of the touch point both in the vehicle and on the test bench.
Once the touch point has been determined and stored in the EEprom memory, the assumption is made that the other parameters that had been initialized with standard values would adapt automatically due to the adaptations during operation.
Such an approach is possible for development vehicles; since a test bench may not always be available to take measurements of the clutch and since there will be no complaints if the vehicle is inconvenient to drive on the first few miles.
However, the problem is that once in serial production, the vehicle is expected to exhibit excellent driving properties from the first mile on. This can only be achieved if all parameters are determined as accurately as possible at the initial start of operation of the vehicle.
In accordance with the prior art, the torque that is transmittable from a clutch can be determined from the clutch position and the speed of the clutch actuator based on a characteristic curve that exhibits hysteresis. The characteristic curve exhibiting hysteresis is based on a simple nominal characteristic curve that is characterized using the following parameters:
Touch point: corresponds to the clutch position in which a torque of 5 Nm can be transmitted.
Friction coefficient: a scaling factor for modifying the gradient of the characteristic curve above the torque of the touch point.
Form factors: scaling factors for modifying the torque values at the nodes above the touch point.
To represent the hysteresis property, the characteristic line is influenced by two further factors:
Position hysteresis: represents a parallel displacement of the modified nominal characteristic curve in the direction of the position as a function of the speed of the clutch actuator.
Torque hysteresis: Superimposes a torque-dependent scaling to the parallel displacement of the modified nominal characteristic curve in the direction of the position. Thus a greater hysteresis width can be attained at higher torques.